1. Field of the Invention
The present invention relates to a communication apparatus, a control method, a program and a computer readable information recording medium, and, in particular, to a communication apparatus which applies the Internet protocol (IP) or such, and applies a technology of logically widening a data transmission band by grouping a plurality of circuits, a control method of this communication apparatus, a program for causing a computer to execute the control method, and a computer readable information recording medium storing the program.
2. Description of the Related Art
Recently, thanks to a sharp spread of the Internet or such, a demand for IP data communication apparatuses increases. Also, a scope encompassed by such a communication network increases. As a result, a data transmission band required for data transmission between respective communication apparatuses included in the communication network may not be completely covered by a physical single circuit. Therefore, it may become necessary to spread a substantial data transmission band by grouping a plurality of circuits, for example. In such a configuration, in order to ensure a required communication quality, a standby circuit may be provided for allocating an extra traffic occurring upon occurrence of a fault on a working circuit.
In a field of data communication, conventionally, a main purpose of the communication is for transmitting images, text, binary data or such, and thus, upon possible occurrence of a fault on a circuit between opposite communication apparatuses, even once lost data may be restored by a technology called ‘retry’ even if several seconds are taken for recovery from the fault. As a result, no substantial problem may occur. However, since delivery of a motion picture, IP telephone communication or such has recently spread along with the widening of the communication band, a distortion may occur in received data when the above-mentioned retry operation is carried out, and such a distortion may directly be sensed visually or acoustically by a user. In such a case, the user may feel artificiality on the delivered motion picture or such.
As a technology for guaranteeing the quality of transmission data even against such a circuit fault trouble, a method of providing working and standby circuits in such a manner of 1+1, n+1 or such is proposed. That is, upon occurrence of a circuit fault, traffic is transferred from the troubled circuit to a standby circuit (or protection circuit). Such a method may be called a ‘protection switching’ method. However, according to the protection switching method, a redundancy in resources is required since a standby circuit is provided as an extra circuit. In terms of saving an investment for such an extra facility, at most one circuit may be prepared as the standby circuit for each working circuit (in an N+1 protection switching scheme, one standby circuit is provided for N working circuits). Accordingly, even when this method is applied, data guarantee may not be completely made if double fault occurrence in a same channel for example.
In order to solve this problem, so-called link aggregation system is proposed in which a plurality of physical circuits are regarded as a single logical circuit (bundle of circuits), and, upon occurrence of a circuit fault, circuit transmission data is dynamically moved among the bundle of circuits (group) and re-configuration is carried out therein, whereby communication is guaranteed. According to the link aggregation system, a basic purpose is that, consequently, a large band is ensured as a result of all the circuits included in the plurality of circuits being always used basically. That is, in this system, a setting is made such that data may be transmitted by each of all the circuits. Accordingly, when a fault occurs in a circuit transmitting data included in the circuit group, a setting operation should be carried out for determining which circuit should be allocated by which the transmission data in the fault circuit is transferred then (re-configuration). As a result, a considerable time may be required, which may amount more than that in the case of the conventional protection scheme.
That is, according to the link aggregation system, a data flow rate is equalized among the respective circuits of the group, and, when a circuit has a trouble, control is carried out to dynamically transfer the data flow rate of the fault circuit. In such a case, hash operation or such is carried out for a normal circuit when occurrence of a circuit fault is detected, and, based on the calculation result, a determination is made for a transmission circuit allocation scheme adapting for a new circuit situation after the circuit fault. Accordingly, an extra time may be required, and thus, a situation may occur in which the required traffic of the communication network may not be satisfied even during a short period.
Japanese Laid-open Patent Application No. 11-154989 discloses a scheme in which, for the purpose of circuit equalization and improvement of transmission efficiency upon carrying out data transmission with the use of a plurality of communication circuits, a transmission data length is counted, and, according to the count result, data distribution to the channels is controlled. According to this scheme, circuit allocation operation is carried out each time when the thus-accumulated data length exceeds a predetermined value, and thus, a circuit load equalization is aimed at. However, this document does not disclose specific process to be applied for transferring signals upon occurrence of a fault on a certain circuit.